Unlocking Database Insights: Listing Tables in PostgreSQL's information_schema

I'd be glad to explain how to list all tables in the information_schema schema using PostgreSQL:

Concepts:

• SQL (Structured Query Language): A standardized language for interacting with relational databases like PostgreSQL. It allows you to retrieve, manipulate, and manage data stored in tables.
• PostgreSQL: A powerful, open-source object-relational database management system (DBMS) known for its reliability, performance, and feature set.
• information_schema: A special schema within PostgreSQL that contains metadata about the database itself. It provides information about tables, columns, data types, users, privileges, and more.

Steps:

1. Connect to PostgreSQL: Use a PostgreSQL client tool like psql (command-line) or a graphical interface (e.g., pgAdmin) to establish a connection to your PostgreSQL server.

2. List Tables in information_schema:

   • Using SQL (SELECT statement): Execute the following SQL query:

   SELECT table_name
   FROM information_schema.tables;
   

   This query retrieves the table_name column from the tables table within the information_schema schema. The result will be a list of all tables in that schema.

   • Using psql command (\dt): In the psql client, type the command:

   \dt information_schema.*;
   

   The \dt command is a shortcut for displaying tables. The * wildcard after information_schema. indicates that you want to list all tables within that specific schema.

Output:

The output from either method will be a list of table names in the information_schema schema. These tables hold information about your database structure, such as tables, views, columns, data types, constraints, keys, and more.

Important Note:

The information_schema schema is a special system schema and shouldn't be directly modified. It's meant for querying information about the database, not for storing application data.

Additional Considerations:

• To list tables in your own schema (not information_schema), omit the schema name in the query or command. For example:

  SELECT table_name
  FROM tables;
  

  or

  \dt;
  

• If you're unsure which schema a table belongs to, you can use the information_schema.schemata table to view all available schemas and their names.

Here are the example codes incorporating the best aspects of both responses and addressing potential issues:

Using SQL (SELECT statement):

SELECT table_name
FROM information_schema.tables;

Explanation:

• SELECT table_name: This part specifies that you want to retrieve the table_name column from the tables.
• FROM information_schema.tables: This indicates the source table, which is tables within the information_schema schema.

Using psql command (\dt):

\dt information_schema.*;

• \dt: This is the psql command for displaying tables.
• information_schema.*: This specifies the schema (information_schema) and uses the wildcard character * to indicate listing all tables within that schema. The semicolon (;) is optional but can be used for better readability.

Both methods will achieve the same result: listing all table names in the information_schema schema of your PostgreSQL database.

While the provided methods using SQL (SELECT) and psql (\dt) are the most common and recommended approaches, here are a couple of alternative methods to list tables in PostgreSQL's information_schema schema:

Using psql command (\z):

This method offers a concise output similar to \dt but displays only the table names, omitting headers and row counts.

\z information_schema.*;

Explanation:

• \z: This is a psql command for displaying table names in a compact format.
• information_schema.*: Same as before, specifies the information_schema schema and uses * for all tables.

Using system catalog view (pg_tables):

While not as portable as information_schema.tables, PostgreSQL provides a system catalog view named pg_tables. This view offers more information about tables compared to information_schema.tables, but it's specific to PostgreSQL and might not be compatible with other database systems.

SELECT table_name
FROM pg_tables
WHERE schemaname = 'information_schema';

• SELECT table_name: Similar to the previous methods, retrieve the table_name column.
• FROM pg_tables: The source table is pg_tables which holds information about tables in the database.
• WHERE schemaname = 'information_schema': This clause filters the results to only include tables belonging to the information_schema schema.

Choosing the Right Method:

• For portability and standardized approach, information_schema.tables (SQL or psql \dt) is the preferred choice.
• For a compact output without headers, psql \z is a quick option.
• If you need additional table information beyond just names (not recommended for general use), pg_tables can be used with caution, understanding its PostgreSQL-specific nature.

Remember, the information_schema schema provides valuable metadata about your database, and these methods help you explore and understand its structure.